The present invention relates to a semiconductor device formed by epitaxial growth, on a semiconductor substrate, of a III-V Group compound differing from the substrate, and more particularly relates to Hall elements possessing the above-mentioned structure.
In the prior art, gallium arsenide (GaAs) III-V compound semiconductors have attracted attention as Hall elements, high speed transistors, laser diodes, light emitting diodes, phototransistors, photodiodes, solar batteries and integrated circuits of such elements because of their properties of high mobility, direct transition band structure, and variability of the band gap and lattice constant by means of 3-element or 4-element compounds.
However, large diameter single crystal gallium arsenide (GaAs) wafers are not easily obtained. Furthermore, the high cost of gallium arsenide (GaAs) type semiconductors is a problem.
Furthermore GaAs is, for example, mechanically fragile compared with Si, the automatic conveyance of large diameter wafers as encountered in the Si wafer process is difficult, and automation of the manufacturing process is very difficult. Although the utility of GaAs semiconductors is recognized, this is one reason why wide industrial utilization has not been attained.
On the other hand, where electronic systems are constructed using each of the above-mentioned kinds of GaAs functionar devices, generally many Si LSI are necessary in the control circuit parts, etc. of the system. Theoretically it is not impossible to make logic IC""s using GaAs, but principally because the formation of a stable insulation layer is difficult, at present there are many problems in constructing IC""s comprising many diverse properties.
Because of this, if the technology were established for monolithically integrating silicon LSI and various kinds of GaAs functions on a single chip, very high function, high added value system devices could be obtained, and furthermore, production by means of an automatic line similar to that in a silicon wafer process would become possible. Needless to say, a large diameter GaAs could be inexpensively produced on a Si substrate or Si IC by using a rough blank with epitaxially grown GaAs up to the required quantity, and development of applications for GaAs could actively expand.
For example, considering the case of a Hall IC, when using a sensor such as a Hall IC it is desirable to obtain the Hall IC by integrating peripheral circuits such as waveform shaping circuits on the same chip as the Hall element. However, when a magnetic detector part is formed as an active layer from silicon, the problem is that the Hall voltage and volume sensitivity are small due to the low Hall mobility.
Hence, high sensitivity and also inexpensive Hall IC""s can be produced by complexing the materials to form Hall elements from high mobility gallium arsenide (GaAs), and form other peripheral circuits from silicon.
However, because the misfit of the lattice constants of silicon and gallium arsenide is large, it has been difficult to grow gallium arsenide of good crystallinity on a silicon substrate.
The present inventors for example, found that in the case of directly growing gallium arsenide (termed GaAs below), which is one kind of a Group III-V compound semiconductor different then the substrate, on a silicon substrate (termed Si substrate below), because of the lattice misfit and the difference in thermal expansion coefficients of the GaAs layer and Si substrate, the problem exists that multiple dislocations, which is to say lattice defects, concentrate in the GaAs layer within a range of 0.5-1.0 xcexcm from the interface of the GaAs layer and the Si substrate; furthermore, close to the interface of the GaAs and the Si substrate the carrier concentration becomes large.
In such circumstances, when the carrier concentration becomes large near the interface having concentrated lattice defects, because current is concentrated in this region, the high mobility of the gallium arsenide cannot be efficiently utilized in the active layer of gallium arsenide grown epitaxially on the silicon substrate. Here, by investigating the mobility of the GaAs layer in the vicinity of the Si substrate, the mobility of this portion of the GaAs layer has been confirmed to be very poor.
As against this, by making the film thickness of the GaAs layer thick, the crystallinity of the GaAs layer is improved, and this is thought to be a method of improving the mobility in the vicinity of the surface of the GaAs layer.
However, sufficient Hall electromotive force could not be obtained even when the GaAs layer has been made thick in a Hall element.
The object of the present invention is to make improvements in the problems of the above-mentioned prior art techniques, to improve the properties of a semiconductor device having a Group III-V compound, for example gallium arsenide (GaAs), as the active layer on a semiconductor substrate being different from the latter, and further, in the case in which the semiconductor device consisting of the above-mentioned structure is utilized as a Hall element, to provide a Hall element in which sufficient Hall electromotive force can be obtained.
The semiconductor device according to the present invention basically adopts a technical constitution as indicated below in order to achieve the above-mentioned objects. Namely:
A semiconductor device possessing a semiconductor substrate consisting of a single element semiconductor; directly formed on the semiconductor substrate, a buffer layer consisting of a compound semiconductor possessing a lattice constant differing from the lattice constant of the single element semiconductor; laminated on the buffer layer, an active layer consisting of the same compound semiconductor as the buffer layer, which functions as a semiconductor element; and, disposed between the buffer layer and the active layer, a barrier layer forming a voltage barrier against the active layer so as to control the flow of current from the active layer to the semiconductor substrate.
Furthermore, in another technical constitution of the semiconductor device in the present invention, it is possible to adopt a semiconductor device in which, in the semiconductor device, the above-mentioned buffer layer is absent, and which possesses a semiconductor substrate consisting of a single element semiconductor; an active layer consisting of a compound semiconductor possessing a lattice constant differing from the lattice constant of the single element semiconductor, this functioning as a semiconductor element; and, disposed between the semiconductor substrate and the active layer, a barrier layer forming a voltage barrier against the active layer so as to control the flow of current from the active layer to the semiconductor substrate.
In the semiconductor devices of the present invention, because they possess such technical constitutions, current is prevented from flowing from the semiconductor element containing the active layer to the semiconductor substrate by the barrier layer, and, because an insulating layer which is capable of making a single crystal of gallium arsenide (GaAs) and insulating the active layer consisting of gallium arsenide (GaAs) is formed on the buffer layer consisting of gallium arsenide (GaAs) formed on the silicon substrate, it is thus possible to insulate the semiconductor element containing the active layer from the high carrier concentration portion which is formed at the interface of the buffer layer and silicon substrate and it becomes possible to improve the properties of the element and to integrate it.
Further, when such semiconductor devices are utilized as Hall elements, it is possible to make the Hall element output voltage VH a voltage equivalent to the Hall voltage with which it is possible to obtain the essential characteristics of a Hall element.